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    <title>Document</title>
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  <body>
    <script>
      // 找出数组中 元素为10的下标，有则打印该下标，没有则打印-1

      // - 例如: [88,20,10,100,50]  打印 2
      // - 例如: [88,20,30,100,50]  打印-1

      let arr = [88, 20, 10, 100, 50]
      for (let i = 0; i < arr.length; i++) {
        // console.log(arr[i])
        if (arr[i] === 10) {
          console.log(i)
        }
      }

      let arr2 = [88, 20, 30, 100, 50]
      let res = -1
      for (let i = 0; i < arr2.length; i++) {
        // console.log(arr2[i])
        if (arr2[i] === 10) {
          res = i
          break
        }
      }
      console.log(res)
    </script>
  </body>
</html>
